1. Field of the Invention
This invention relates to high temperature process, i.e. an "Ene" process, for producing oil-soluble derivatives of a monoethylenically unsaturated C.sub.4 -C.sub.10 dicarboxylic acid material under conditions of reduced sediment formation as well as to the resulting substantially sediment-free product useful for preparing ashless dispersants untilized in lubricating oil and fuel compositions. In particular, this invention is directed to a sediment-free process involving the "Ene" reaction of a polyolefin and maleic anhydride to provide a precursor for the production of lubricating oil and fuel additives wherein said reaction is carried out in the presence of a sediment-preventing amount of an oil-soluble strong organic acid.
2. Description of the Prior Art
During the past several decades, ashless sludge dispersants have become increasingly important, primarily in improving the performance of lubricants in keeping the engine clean of deposits and permitting extended crankcase oil drain periods while avoiding the undesirable environmental impact of the earlier used metal-containing additives. Most commercial ashless dispersants fall into several general categories.
In one category, an amine or polyamine is attached to a long-chain hydrocarbon polymer (the oil-solubilizing portion of the molecule), usually polyisobutylene, through an acid group, such as a dicarboxylic acid material, e.g. succinic anhydride, by forming amide or imide linkages.
In a second category, an alkanol or polyol is attached to said long-chain hydrocarbon polymer through said acid by forming an ester linkage.
In yet another category, the reacton products of hydrocarbon-substituted succinic anhydride, e.g. polyisobutenylsuccinic anhydride, with compounds containing both an amine group and a hydroxy group have been suggested as useful or investigated in the prior art.
The common reactant in all said categories is the long-chain hydrocarbon polymer attached to a dicarboxylic acid group. The polyolefin diacid is readily obtained via the dehydrohalogenation, Diels-Alder or "Ene" reaction of an olefin or a chlorinated olefin with an unsaturated C.sub.4 to C.sub.10 dicarboxylic acid, anhydride or ester thereof, such as fumaric acid, itaconic acid, maleic acid, maleic anhydride, dimethyl fumarate, etc. The dicarboxylic acid material formed via the Ene reaction of an olefin with maleic anhydride results in an alkenyl-substituted anhydride which may contain a single alkenyl radical or a mixture of alkenyl radicals variously bonded to the cyclic succinic anhydride group. This "Ene" product is a preferred precursor for said ashless dispersants since it does not contain any halogen which could be a source of undesired activity when said dispersant is incorporated into the lubricant or fuel.
Unfortunately, the "Ene" reaction of an olefin and maleic anhydride is difficultly reactable and/or results in extensive sediment formation believed to be primarily poly(maleic anhydride) and decomposition products of maleic anhydride.
The deleterious effect of metal ion and alkyl amine contamination upon molten maleic anhydride has been reported, by Vogler et al in the "Journal of Chemical and Engineering Date", Vol. 8, No. 4, pgs. 620-623 of October 1963 entitled "Effect of Contaminants on the Thermal Stability of Maleic Anhydride", to include heat and gas evolution and a solid polymeric material. The structure of poly(maleic anhydride) was the subject of a paper by R. Bacskai, which appeared in the "Journal of Polymer Science", Vol. 14, 1797-1806 (1976) and which teaches that polymerization can be initiated with free radical catalysts and results in the evolution of CO.sub.2. The "Ene" reaction of olefins having from 12 to 18 carbons with maleic anhydride to prepare alkenyl succinic anhydride has been conducted in the presence of inorganic acids, anhydrides and salts thereof such as boron phosphate (see German Patent Application No. F 10267 IV b/12 published Sept. 6, 1956).
Another "Ene" reaction of olefins having 6 to 24 carbons with maleic anhydride to prepare said alkenyl succinic anhydrides is carried out in the presence of phosphorous containing sequestrants and hydroxy aromatic compounds for the preparation of detergents of improved color, i.e. reduced colored polymeric byproducts.
The suppression of polymeric byproducts arising out of the Ene preparation of alkenyl succinic anhydrides is reported in U.S. Pat. No. 3,819,660 to be achieved by the presence in the reactor of a C.sub.1 to C.sub.3 alkyl-substituted benzene sulfonic acid (preferably as a solute in acetic anhydride) and in U.S. Pat. No. 4,086,251 by the presence in the reactor of a halogen-containing additive.
Thus, the prior are teaches the "Ene" preparation of alkenyl succinic anhydrides but unfortunately with excessive sediment formation, which sediment appears to be at least in part deleterious poly(maleic anhydride). Further, some of catalysis scavengers and sequestrants which are used in the preparation of alkenyl succinic anhydrides are detrimental for lubricating oil applications in that solid materials are corrosive and/or are oil-insoluble thus contributing to haze and/or sediment.
It is therefore an object of this invention to produce alkenyl succinic anhydrides by the Ene process with reduced sediment formation through the influence of a lubricating oil-soluble material.